In reply, WBHS needed just two runs from two balls after a strong 39 from Luke Trigg. But a late run out scuppered their efforts after Matt Lobb (3 for 16) and Harry Darkins (3 for 21) restricted their scoring.
In their second outing City grabbed a 24 run win over Maungakaramea after a 34-ball blitz from Ian Page.
Page smoked 83 in no time to lead City to 154 for six despite the best efforts of Raman Sharma (3 for 19).
Maungakaramea scored just 130 for 8 as Sam Murphy top scored with 34.
Onerahi meanwhile started their day with an eight-wicket win over Maungakaramea after restricting them to just 84.
Fletcher Coutts led the way with classy bowling figures of 5 for 15 from his four overs.
Todd Beehre's unbeaten 35 helped Onerahi to victory with five overs to spare.
Onerahi then grabbed a seven-wicket win over Kamo to prove their credentials as a must-beat side.
Kamo scored 103 for five from their overs with Lakhvir Singh leading the way with 41.
Onerahi picked up a pair of run outs while Tom Herman (2 for 17) was the pick of the bowlers.
In reply, Dominic Finn (31 not out) and Coutts (39 not out) made light work of the total, getting home with over five overs remaining.
Kamo had some earlier success as they grabbed a five-wicket victory over Kaipara Flats.
Kaipara Flats scored 124 for four in their innings as Liam Wewege (43) and Liam Jones (41) provided the majority of the scoring.
In reply Dante Mitchell made fairly light work of the target with his unbeaten 55. Jones (2 for 12) was economical but couldn't do enough to secure the win for his side.
The final match between WBHS and Kaipara Flats was a low-scoring affair as Kaipara couldn't find their feet with the bat.
Jones added 28 but they were bundled out for just 56 as Kurt Oldridge (2 for 11) and Sam Webb (3 for 6) tied them down early.
WBHS cruised home as Sweeney hit 28 to secure the eight-wicket result.
Next week's fixtures will decide who plays in the final on January 21. Onerahi take on Kaipara Flats, City face Kamo and WBHS do battle with Maungakaramea.